The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.
Currently, a typical tailfin deployment and locking system in a flying object, used to impart stability to the flight of the object, utilizes large aft-housing lug 312 and small forward-housing lug 313. These lugs are located on housing 201 of flying object 101 and serve the purpose of reducing the housing area required to attach and deploy fin 202. The fin itself has, extending from its body, rear boss 309 and front boss 311 which work in conjunction with the housing lugs to lock the fin in position once the fin has reached the desired deployment position. More specifically, combination torsion/compression spring 204 acts between the fin and the housing to rotate the fin from its initial folded position on the housing to its deployed position and to lock the fin against the aft-housing lug. A rebound stop formed into the aft-housing lug prevents over-rotation of the fin.
An example of such fin deployment and locking system usage can be found in the multiple submunitions which are commonly referred to as xe2x80x9cBATsxe2x80x9d and are carried in the Army Tactical Missile System (ATACMS) missile 100 as shown in FIGS. 1A and 1B. As stated above, currently, in the BATs, or other similar flying objects 101, a combination spring is used which provides both the torsion and compression spring functions. The combination spring is made from multiple turns of a steel music wire of a given diameter to generate the desired in-lb/degree of torque and lb/in of compression. The torsional effect of the spring rotates the fin to open to deploy it from its closed or folded position while the compressional effect holds the deployed fin in its deployed position against the fin stop. The fin stop is small flat shelf 314 on the aft-housing lug designed to stop the rotation of the fin by engaging a cut-away area (not shown in the drawings) on the fin""s rear boss and prevent the fin from rebounding. But the forces generated during the initial impact of the fin with the shelf frequently overcome the spring forces, causing the fin to rebound before finally locking into its deployed position. The small forward-housing lug acts as a guide to keep the leading edge of the fin aligned correctly during deployment and in the correct position during flight of the object, but is not intended to be a load-carrying member.
The current state of the art in fin deployment and locking system as described above with respect to the BAT as an example suffers from two major problems: The first is that the fin does not reliably slide aft, this failure causing a corresponding failure on the part of the cut-away area (not shown in the drawings) on its rear boss to engage the shelf on the aft-housing lug on the initial deploying stroke of the fin. This absence of reliability allows the fin to rebound from the shelf as many as two or three times before the fin slides aft enough to engage the locking mechanism. In an aerodynamic environment, such repeated rebounds can promote fracture of the fin root and even cause loss of control of the flying object; the second problem, closely related to the first, is the lack of sufficient strength in the forward-housing lug to withstand the additional forces imposed on it by the repeated rebounds of the fin. The forward-housing lug is not designed to carry any load.
The improved fin lock system overcomes the major problems associated with the current deployment and locking mechanism by adding a center boss to the fin between the rear and front bosses and a sliding lock that engages between the housing and the center boss. The sliding lock, having a very low mass, engages with the center boss, and thus with the fin, very quickly and reliably when the fin reaches its fully deployed position, thereby arresting the motion of the fin and preventing it from rebounding. This, in turn, allows the aft-housing lug to lock the fin in its deployed position with one opening motion of the fin.
The actuation of the fin is accomplished by a torsion spring that rotates the fin to the deployed position and a compression spring that moves the fin into the locked position. The addition of the center boss and sliding lock not only provides a secure locking but also increases the strength of the fin by preventing the fin from over-rotating, thereby reducing the bending moment on the fin. Further, the stresses on the aft-housing lug are reduced by the center boss""s additional support of the fin.